Sequential Circuit's Forgotten Past...The Model 700 Programmer

Before they became world famous for creating the Prophet 5 synthesizer, Sequential Circuits built accessories for popular synths. An interesting and under-appreciated one is the Model 700 programmer. Designed to be hooked up to a Minimoog ( or other CV controlled synth) it's easy to see how this unit was the seed of the concept that eventually led to the creation of the P5.
Print ads from back in the 70's show the unit along with Sequential's other product at the time, the model 800 Digital Sequencer. Here's an early ad featuring no less than Undisputed Minimoog King Rick Wakeman, not too shabby of an endorsement for a fledgeling company that at this point appears to be based at yet another interim address in Silicon Valley, possibly one of Dave Smith's apartments.

Companies did a fair amount of wanderin' back in those days, it would seem.


These devices both offered an interesting alternative to what Oberheim was offering at the time. Oberheim had been building a digital/analog hybrid sequencer since 1974, and offered a rudimentary programmer as an addition to their four and eight voice polyphonic systems, but not as a stand alone device to control other synths.



The address for this ad shows yet another location for the early operations of the company before they settled into their main headquarters on North First Street in San Jose...


...After which, one assumes that they had a nice party to celebrate. The Digital Sequencer was apparently well-shielded against such real world hazards as cake frosting and delicious candies, while the Programmer appears somewhat less ready to deal with such tasty dangers.

The unit has 64 user definable presets to control various key aspects of the host synthesizer.
There are three quantized CVs that can control oscillator pitch, and two programmable envelope generators (including delay) that can control the filter and final VCA. Switches for each oscillator allowed the inclusion of an external CV source like a sequencer (perhaps the Model 800, eh?) and the filter envelope section included an offset control for initial filter tuning. Although there's no way to set various wave forms or mix or mute individual oscillators, this was still a big step forward for those Brave Souls grappling to successfully control a Minimoog or the like in the heat of a live performance.

Imagine the pressure...

"Tune Those Oscillators!"

"Trim That Filter!"

"Adjust Those Attack and Decay Times!"

"Flail Randomly at that Keyboard!"

"Dance, Monkey Boy, Dance!!!"



If you hold your head at the proper angle and squint your eyes at it just so you can sort of see some the control panel for the P5 lurking there, just under the surface.



I picked up my first Model 700 in Sacramento in the early 80's, where I found it sitting dusty and unloved in the corner of a store, for $75. I used it to give the Moog 55 some quick programmability, and got a fair amount of fun out of it over the years. It was easy to connect into the system in various ways since it was equipped with 1/4" jacks, and the programmable DADSR envelope generators were a nice addition, although the programmable steps (64 for each segment) were a little coarse. I couldn't resist customizing the preset selector switches with color coded ones, to match what I had done with my Prophet 5 (more on that in a future blog).




To get the maximum amount of control with a Minimoog required some modification of the instrument, and typically a multi pin connector was added to match the one provided on the back of the Model 700. This made connecting things quick and easy, but the hassle and expense to get this done probably discouraged some potential customers at the time (not to mention the units $1200 price tag).

Back then, for a few hundred dollars more, you could actually buy a Minimoog.


I remember reading that Howard Leese used one with Heart, and I can see him wailing on a Minimoog during "Magic Man" in my mind's eye as I look at this unit.



An interesting performance feature is a footswitch jack that lets you step through the presets, a great idea. There's a front panel knob that sets the number of steps (1-8) the unit will cycle through in a bank, so you could preprogram a manageable sized preset cluster to jump around through during a song if desired, without having to take your hands off the keys. It's Magic, Man!

Now, if you look at this feature set closely, it begins to look more and more familiar.

Hmmm....programmable voltages, switch steppable, selectable cycle length...

Hey, It's an (up to) 8 step sequencer!

Each step has 3 quantized pitch CVs, and two programmable envelope generators, as well as filter and VCA settings, making this this a pretty powerful sequencing tool. The footswitch input is even switch selectable to accept V or S triggers. What more could a young synthesist need?
Let the Sequencing begin! Yee-Haaa!




Well, in reality, the stock unit took a finite amount of time to update all the parameters when switched, which made running faster sequences tricky, as you could often hear the pitches slewing to reach the notes in time.

I got a schematic for the unit (mucho thanks again, Riley!) and noticed that the design was pretty straightforward...no microprocessors here! I found that by speeding up the system clock, I sped up the overall response time, which reduced the slewing effect at faster sequence speeds. I carefully adjusted the clock for the fastest performance possible without things going horribly awry during preset changes, and this boosted the usable sequencer speed considerably. Not as blazing fast as the Moog 960, but reasonably zippy nonetheless, and with the wealth of features available and some thought and planning, the sequences could be incredibly deep and detailed.


For those looking for even more control, a simple mod allows the internal Delay CVs to be routed to a set of jacks on the back, providing the user with two more programmable CVs per step. By using a normalled jack for this, the Delay function of the DADSR generators is available until you plug in a cable, which sets the delay to zero and makes the CV available for other nefarious purposes in your system. Push that pulse width? Bully a VCO? Totally programmable System Transposition per step?

Hey, WHY NOT?!!?

Besides, how often are ya gonna actually use that delay function, Chukko?


An interesting quirk of the unit is that the rotary selector switches have positions that are unused, and just labeled as OFF (maybe they got a good deal on the extra position switches). The step position selector was like this, so I decided to press these unused positions into service somehow.



After some tinkering around, I devised a circuit that could switch preset banks at the end of the 8 step sequence (much like using the sequential switch on the Moog 55) so now the unused rotary switch positions could be used to select a longer sequence by combining banks, making 16, 24, 32, up to full 64 step sequences possible.



Now this was starting to become a pretty formidable sequencing tool, as well as a super cool programmer.

Who knew?



There were two versions of this unit produced during its lifetime. My first unit was the later version, which had some improvements and used SSM voltage controlled envelope generator chips and VCAs to handle the programmable side of things.

Years later, I discovered that there was an earlier version, when I picked one up in a store in San Jose, also at a very reasonable price (thanks, Barney!). This one had engraved numbered preset selector buttons, and a discrete component envelope generator inside, probably predating the ready availability of the SSM chip.





As you can see, this is a pretty early example (SN15!!) almost certainly built in Dave Smith's apartment (you can almost see him at his kitchen table laboring deep into the night soldering the circuit boards by hand...) The board and component assembly looked much more, er, rustic with a more California handmade/organic quality to it.

The Waves sticker on the back is an interesting touch...I've never been able to find any info on them, but the thought of good Napa Valley wine and synthesizers is a very appealing combination. Any info out there, anyone?

This one I've left stock. Particularly interesting is the large number of CA3080 progammable OTA chips inside, being used as the many sample and hold cicuits and VCAs for the various CVs inside.

Dig all that OTA goodness, Bunkie!



Not to mention the gold-plated diapers, babies!

Woof!




"I've gotta fever, and the only prescription is MORE SCI 700!!"

The Secret World (And Surprising Hidden History) Of The Moog 960 Sequencer!

This particular blog entry started simply enough.

As you probably already know, Moog is making a limited run of their Modular systems, including the 15, 35, and 55, as well as the Sequencer Complement B.

An incredible feat, and I could scarcely belive my eyes when I saw this announcement (and the entire Analog Resurgence from Sequential Circuits and others) at the NAMM show earlier this year. For a few moments, I worried that I was actually having a stroke, and this was what my sputtering and sparking brain was coming up with to try and entertain me in the interim...("Hey, it's actually 1974, and everything's going to be just fine, so don't freak out, OK??")

 

I saw a thread on a forum recently where someone was asking why the sequencer was so expensive ($8500). A lot of hoopla erupted after that, with people alternately trying to explain why something like this might cost what it does, and others declaring that this was nothing short of highway robbery, and they'd much rather have their brand (insert name here) sequencer which is just as good, or maybe better, and just who does Moog think they are, anyway?!??!!?

As I continued to read through this thread, I thought that maybe I should profile the 960 sequencer next, and provide some pictures showing the high level of craftsmanship and quality that actually went into creating this excellent and iconic piece of technology, so I removed it from my System 55 and started taking some pictures of it, and that's when things began to get really interesting (more on this in just a bit)...

Now, to put things into perspective, the Sequencer Complement B is actually a collection of two 960 Sequencers, mated with two 962 Sequential Switch modules, a 961 Trigger Interface module, and a 994 Dual Multiples module all contained in a beautiful solid walnut extension cabinet. A serious amount of handbuilt technology for a serious amount of money?

 

Well, back in 1974, this same setup went for $3,295, and rightfully so. An inflation calculator will show that in today's dollars, this would now cost $15,894!!!

Suddenly, the $8500 price tag begins to look a bit better...

 

It's certainly not difficult to see why these would cost what they do, given the cost of components these days that would be used, the amount of effort required to locate and procure them, and the sheer amount of hand labor that goes into creating something like the 960 Sequencer. I haven't seen one yet, but Moog claims (and I have absolutely no reason to doubt them) that they will be making these modular systems and assemblies using the same components and manufacturing techniques that they used in 1974. This is almost unheard of in this day and age, and shows their commitment to getting this reissue right...for those that can afford it, of course.

Take a look at the beautiful wiring looms that are required to connect all of the components together. This would be difficult to make if you were already experienced at making these, and did this every day, for years. Now imagine that you have to recreate this starting from scratch, and the task begins to take on some weight...there's a lot of stuff to get right.

Boards will be created from the original artwork and lovingly hand-stuffed just like in the old days, using period correct components, photo etched front panels, etc, etc.

The switches are very difficult to come by these days, and expensive, and the pots...don't even get me started on the pots!!!

Allen Bradley hasn't made these type J series pots in years, but back in the day they were considered the absolute top shelf component, Military Grade, and they were expensive even back then.

It's a testament to their quality and ruggedness that every one of them in my 55 modular is still working 40+ years later. Switches too!

The Canadian company PEC makes what I would consider to be the closest currently available replacement, and even these run around $15-$20 each.

The 960 sequencer uses 25 (!) of these.

Almost all of the circuitry that powers the brain of this system has been out of production for years. The chances of finding replacement chips for these are low, which means that they will cost many times their 1960s-1970s prices (cheap enough back then, not so much now). These are Motorola RTL chips, an early type of digital logic chip.

As you can see, the 960 Sequencer uses a fair number of them, as does the 961 Trigger Interface and the 962 Sequential Switch modules. Major Kudos to the good folks at Moog for marshalling the resources to make these incredible instruments available again. How the heck did they do it?

 

 

And now, on to the Hidden History part of today's Feature Presentation, which is already in progress...

Hey! I've owned my System 55 for 30+ years, and gleefully modded various parts of it as well as performed all my own maintenance of it, and I only now realize that I've taken certain parts of it for granted.

Even in this sophisticated system, there were still sections of it that were hand built on perfboard (!) for certain functions. My system 55 is a pretty early one, and it seems that these hand-built boards were created like this before finished printed circuit boards were available.

The CP3A mixers were built this way...

Boards that do Trigger buffering...

 

...As well as hybrids like the attenuverter for the 904 filter...a circuit board grafted to the board that power is connected to.

 

I've seen pictures on the web of other modules that were more or less hand made, and after spending time modifying and refurbishing sections of the modular many years ago, I sort of ignored these oddities.

In less than a year, Moog was building the 55 modulars with actual printed circuit boards in these locations. Here you can see these boards in a later model. Notice that the individual hand-matched 100k ohm summing resistors have been replaced with a resistor network package for both the CV summers and the CP3A mixers (those light blue rectangular packages).

 

As I was taking some close up pictures of the sequencer, this (finally!) caught my eye...

What The What??!!!?!?

I'd always assumed that this was just another factory hand built module, but as I was paying more attention to it while photographing it, I suddenly realized that this board really didn't look like any other Moog handmade boards, and looking carefully at the opamps revealed a datecode from 1976,

after the module was built at Moog, and purchased by the college.

So now, a new facet of the history of my system had been revealed...it had been modified by someone while it was still at the college!

 

The board appears to duplicate the circuitry for each of the three analog voltage outputs of the sequencer using 308 opamps (a very good opamp at that time) to replace the discrete component opamps that were being used at that time on the sequencer. This would make the output voltages less sensitive to drift with temperature changes, and make it more stable, especially for live performances where temperature changes are likely more pronounced.

 

This is what the discrete component opamps would have looked like before all the circuitry was removed and replaced with the current board assembly...

 

The quality of the work is pretty good, which is probably why it never attracted my attention before. The area where the original circuitry was has been completely depopulated, and the board was nicely cleaned to remove any flux and solder left behind...a very pro job.

 

It makes me wonder if the work was done locally by a teacher or student, or if it was shipped off somewhere to be professionally modified. There were places in the 70's that specialized in performing modifications to synthesizers, although I can't recall reading about anyone performing this particular mod. I'd love to hear from anyone who might recognize this or have more information about it!

The only things I would have done differently would be to use low drift cermet trimmers like the Bourns 3362 in place of the carbon Piher ones that were used, which would make it even more stable.

Yeah, I know...picky, picky.

Trimmers like these were certainly much more expensive and less available back in the mid 70's, and even Moog used cheaper carbon trimmers in their original discrete component version.

 

After finding this, I began to wonder if there were other mods that I had glossed over as well, so I began to look at the other modules in my system with a fresh perspective.

 

I didn't have to look far.

 

The same discrete opamp circuit was used in the 962 sequential switch, and sure enough, there was the same replacement board installed in its place, a true chip off the ol' block.

This one used a precision multiturn trimmer (a nice touch) and the same board material and datecoded opamp. These were likely modified together, and a very nice job they did of it, too!

 

Now my curiosity was up. I had another 962 sequential switch that I has gotten quite a while ago from a friend, same circuitry but a different front panel layout. This panel was the same size as the one for the power switch and pilot light in the lower right corner of the main cabinet, so I had moved the power panel to the rear of the unit, and installed the much more useful sequential switch in its place.

Looking at the board for this unit, I found this...

 

Same idea, but an even more elegant implementation...a handmade etched and drilled printed circuit board, also complete with the 308 opamp. Whoah! It's apparently a thing, I guess.

Am I the only one who doesn't know about this?

 

 

Again, some nice low drift cermet trimmers certainly wouldn't be out of place here, but there's not much else to improve this groovy little mod, which apparently, has occurred to more than one set of crafty hands...

 

 

 

 

 

 

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Gettin' Some Serious Control Of The Moog 55 Modular!

The next round of modifications For the Moog 55 came about to increase the system's usefulness in studio and live performance.

Although the 55 looks like a very large and powerful system, there are some things about the way it's implemented that limit its abilities, and not always in ways that are immediately apparent.

Well, some are obvious. Seven VCOs and ONE lowpass filter? I mean, C'MON.

But hey, that's a pretty obvious one, and you knew the job was dangerous when you took it.

Sure there's also a highpass filter, but on its own, it doesn't give a lot of flexibility for voice shaping. There's a set of 6dB/octave lowpass and highpass rotary switches that I still haven't figured out much use for even after all these years (and I'm certainly open to suggestions here).

There's other things that are less obvious, but pop up as annoying limitations as you use the system more and more.

For instance...

Hey, there's no real dedicated LFO. Sure, there's the big standalone 921 oscillator, but using it as an LFO seems like a criminal waste of its many capabilities. It's the only oscillator in the system that can be hard synced via the Clamp input, and who wants to give up an incredible audio oscillator as a lowly LFO anyway?

On the other hand, it is syncable and resettable when used as a clock, and the adjustable differential auxiliary output makes for great stereo panning effects when patched to a couple of VCAs, it has a reverse sawtooth output...maybe it IS just a very capable (and expensive) LFO. It's puzzling. At any rate, where are the simple LFOs? Not here...

 

The 921B oscillators can be set low enough to be an LFO, but each of the two banks of 921B oscillators are tied to a single 921A controller. You can't use the other two oscillators as audio oscillators tracking the keyboard without the third (LFO) oscillator tracking the keyboard as well. What the what??!??!

 

Yes, that's right...there is NO way to control these oscillators individually! There's no separate CV tracking inputs, and no way to separate them from the 921A controller. So in reality, instead of having 7 oscillators in the system, you have 2 groups of 3 oscillators that must track the same pitch CV (so basically you have two fat oscillators) and one super oscillator that will, in most instances, end up being an LFO.

Erg.

This was a sobering realization as I started trying to create larger independent patches.

Another hidden limitation is that all three 921B oscillators in a group share the same pulse width, and the same amount of PWM if applied. If you set the 921A controller so that one oscillator is a square wave, all three are square waves. There are no individual CV inputs for pulse width on the 921B modules. When you consider just how useful poly PWM is for creating lush animated leads and pads, this becomes a baffling omission for a top of the line system.

Even the MiniMoog lets you set separate pulse widths for each oscillator, and even though they don't have PWM, there are certainly some classic sounds to be had there.

Now, to be completely fair, all of these things I've listed here as limitations actually tend to underscore what was still the main purpose for this system back in 1974.

It was designed as a studio instrument, where you would use recording techniques like overdubbing to build up a complex sound, instead of having lots of individual control of all the basic elements. While I could see and understand this approach to using the instrument, I was increasingly missing the touches that would further unlock the many capabilities that lurked beneath the surface, tantalizingly out of reach. And for live performance, having this kind of flexibilty greatly increases the usefulness of the system, since it can be patched to do more at once.

So, here's what I did about it (deep breath).

 

The schematics show that each 921B already has the necessary circuitry to be controlled by multiple CVs for both the pitch and the pulse width. The only thing required would be a summing opamp circuit for each, an easily implemented circuit. This would duplicate the actions of the summing circuits in the 921A...in essence giving you two (or more) separate control inputs to these oscillators. This seemed like a promising place to start...

 

I also needed to create some jacks as inputs for these new CVs, but the oscillator panels are already filled with jacks, and I didn't want to lose any of the current sync or FM capabilities.

My solution was to replace the mono jacks used here with TRS stereo jacks. Now, if I plugged a cable in halfway (first click) then the incoming signal would go to the original sync or FM destination. If I plugged the cable all the way in, then the signal would go to the new pitch or PW destinations. I could use a TRS splitter to drive both destinations at once if desired, and best of all, the mods would be invisible from the front panel.

 

 

I designed and built the additional summer boards using surface mount technology. This gave me a very small footprint, as the circuitry is fairly simple, and allowed me to use some very beneficial components.

With pitch inputs to summers, the input resistances must be very closely matched to tolerances of .1% or better to get proper tracking from multiple CV sources (like if you planned to drive an oscillator from a sequencer and also a keyboard to make transposition changes). Companies back in the day like Emu Systems or Sequential Circuits often had someone dedicated to measuring and binning vast quantities of 100k ohm metal film resistors all day long to feed production needs, using accurate test meters or a specialized test setup.

For my summers, I opted to use precision surface mount thin film resistors from Susumu that are already factory matched to .01%. These excellent resistors cost a little more, but the end results are worth it. I also chose a surface mount precision low drift dual opamp for my design that served as both the pitch and PW summers. All of this was built onto a Surfboard 9161 prototype board including a fine tuning trimmer for the pitch CVs.

Now, I know that there are some people who are wary of their abilities to solder surface mount components, but with good equipment, practice and patience, it's not really that difficult, and the end results can be quite good.

 

There was even enough room at the bottom to drill a small hole to allow for mounting the boards on the oscillator module via a stick-on nylon standoff.

 

As I thought about how I might use this, it occurred to me that it would also be useful to be able to disconnect the CVs coming from the 921A to increase the amount of independent control for each oscillator. For this, I decided to add a set of small switches to each 921B for the pitch and PW controls coming from the 921A. This way, each oscillator can be controlled from an external CV, the 921A, or both!

Hey, now we're gettin' there!

 

 

After carefully selecting and drilling the locations on the oscillator front panel, I installed a pair of short bat toggle switches. Using a nice dress nut instead of the standard supplied hex ones made them look more like original equipment on the panel.

These switches connect or disconnect the pitch and PW summing signals from the local 921A module for each oscillator.

After a bit of tweaking and tuning, each oscillator worked great, and was now completely addressable from any internal or external CV sources.

 

And, everything looked great installed back into the system as well, I think.

 

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